A fully narrated documentary like Cosmic Voyage uses a voice over to guide the audience's understanding of events. Documentary dramas like Deadly Women recreate real events through reenactments. A fly on the wall documentary such as The Airport is mostly observational with little commentary or narration. Self-reflexive documentaries like Deadly 60 feature the filmmaker speaking to the camera to engage the audience. Mixed documentaries like Britain’s Trillion Pound Island employ interviews, observation, and narration to advance the creator's perspective. Documentary soaps follow groups of people through eavesdropping and require no cast, making them inexpensive to produce.